This invention relates generally to dies for applying hot melt adhesives to a substrate using meltblowing, spiral, bead, spray, or coating patterns. In one aspect, the invention relates to modular die bodies with interchangeable and replaceable die tips or nozzles. In still another aspect the invention relates to an inexpensive disposable die module.
The deposition of hot melt adhesives onto substrates has been used in a variety of applications including diapers, sanitary napkins, surgical drapes, and the like. This technology has evolved from the application of linear beads such as that disclosed in U.S. Pat. No. 4,687,137, to air assisted deposition such as that disclosed in U.S. Pat. No. 4,891,249, and to spiral deposition such as that disclosed in U.S. Pat. Nos. 4,949,668 and 4,983,109. More recently, meltblowing dies have been adapted for the application of hot melt adhesives (see U.S. Pat. No. 5,145,689).
At the present, the most commonly used adhesive applicators are intermittently operated air assisted dies. U.S. Pat. No. 5,618,566 discloses a modular die assembly comprising a row of side-by-side modules mounted on a manifold. Each module is provided with a die tip or nozzle through which the adhesive is extruded. U.S. Pat. No. 5,728,219 discloses a modular die assembly comprising side-by-side modules mounted on a manifold. Selected modules of the array may be provided with different types of extrusion die tips or nozzles. The term "nozzle" is used herein in the generic sense to describe the part of the applicator which determines the pattern of adhesive deposition (e.g. spray, bead, spiral, coating or meltblown). The nozzles for bead and spiral deposition are adapted to deposit a monofilament onto a substrate. The nozzles for meltblown applicators, also referred to as die tips, are designed to meltblow a row of filaments onto the substrate. Nozzles for bead and coating deposition are non-air assisted.
The availability of different types of nozzles for each module permits the operator to select a variety of deposition patterns. Each of the nozzle types has its own advantages and disadvantages. Meltblown nozzles provide a generally uniform covering of a predetermined width of the substrate, but do not provide precise edge control which is needed or desirable in some applications. On the other hand, the spiral nozzles deposit a controlled spiral bead on the substrate giving good edge control but not uniform substrate coverage. The bead and coating nozzles provide a heavier adhesive deposit than the meltblown or spiral patterns.
In order to replace a nozzle of a particular die module in the die assembly disclosed in U.S. Pat. No. 5,618,566, or change a nozzle type of a module in the die assembly disclosed in U.S. Pat. No. 5,728,219, it generally is necessary to (1) remove the module from the manifold (2) unscrew the four bolts mounting the nozzle assembly to the module, (3) substitute the new nozzle for the old nozzle, (4) resecure the nozzle assembly to the module, and (5) reattach the module to the manifold. Although this is a simple procedure compared to the non-modular die constructions, it nevertheless requires some shutdown time (on the order of 30 to 60 minutes). For this reason, the entire module is generally replaced and the old module repaired.